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Laser Machining of Metals
Published in V. K. Jain, Advanced Machining Science, 2023
The material capable of sustaining stimulated emission and amplifying it is called gain medium. For stimulated emission to occur, the gain medium must be supplied with external energy to pump atoms from the ground state to an excited state, also called pumping. Pumping is essential in creating a population inversion, wherein the number of atoms in the excited state is more than that in the ground state. Pumping is typically done using electrical or optical energy. The most common pumping sources are a flash lamp or another laser source. Population inversion is necessary for the gain medium to amplify light produced by stimulated emission. Light amplification is achieved by providing optical feedback by placing a pair of mirrors on either side of the gain medium, as shown in Figure 7.2. The mirrors could be flat or curved. The setup is known as an optical cavity or a laser cavity. Light confined in the optical cavity bounces back and forth upon being reflected by the mirrors, producing standing waves. Every time the light passes through the gain medium, it gets amplified. One of the mirrors is fully reflective, while the other is partially transparent (output coupler), thus allowing some light to escape the optical cavity, generating a laser beam. The laser wavelength depends on the type of gain medium used, which could be a gas, liquid, or solid. Examples of gain medium include ruby crystal, CO2 gas, helium-neon gas, Nd: YAG crystal, doped-fibers, etc.
Packaging and Assembly of Microelectronic Devices and Systems
Published in Anwar Sohail, Raja M Yasin Anwar Akhtar, Raja Qazi Salahuddin, Ilyas Mohammad, Nanotechnology for Telecommunications, 2017
Laser diodes, as the name indicates, are LED-type devices capable of producing a spatially coherent, narrow, low divergent beam of light using stimulated emission on a semiconductor scale. Stimulated emission is effected by providing a gain medium within the laser diodes. The gain medium is a material with properties that allows it to amplify light by repeated reflection of photons until they gain the energy required to leave the material. Typically, a thin layer of AlGaAs sandwiched between P-type and N-type AlGaAs layers acts as the gain medium. The P-type and N-type AlGaAs layers are in turn sandwiched between a P-type and N-type GaAs to form the most commonly used laser diode, referred to as the injection laser diode or the quantum well separate confinement heterostructure (SCH) laser diode. The term injection refers to the electrons that are pumped into the device through the P-type material. The quantum wells within the gain medium represent the nanostructure within this optoelectronic device. The refractive index of the GaAs layers is lower than the inner layers thereby containing the light effectively within this region, which allows for effective stimulation. Also, the ends of the heterostructure device are polished to act as mirrors to reflect the photons back into the gain medium for more recombination or stimulation. Typically, one of the mirrored surfaces is partially transparent and the output laser beam is emitted through this surface on the side (Figure 14.10).
Finite-Difference Time-Domain Method Application in Nanomedicine
Published in Sarhan M. Musa, Computational Nanotechnology Using Finite Difference Time Domain, 2017
Laser is a well-known technology at present. It is presently used in several applications [84–91]. Briefly, laser is a device that deals with light; hence, it is an actual application that deals with electromagnetic waves [84–91]. The process of light manipulation is the basic principle of any laser device [84–91]. The device firstly emits the electromagnetic radiation, light, through a specific process called optical amplification to get the desired laser [92,93]. During modification, the stimulation of photon emission is done [84–91]. Basically, a laser device has to consist of a gain medium, which is needed for energy supply [92,93]. Also, a laser device requires the optical feedback portion [92,93]. The gain medium is a specific material allowing light amplification. The emission stimulation is used as already mentioned. The stimulating process is done on a specific wavelength within the gain medium aiming at amplification to increase the power [92, 93]. Based on the already described process, there is no doubt that laser devices can provide energetic light that can be used to attack.
Use of lasers in minimally invasive spine surgery
Published in Expert Review of Medical Devices, 2018
The term ‘laser’ is an acronym for light amplification by stimulated emission of radiation [15,16]. Lasers differ from other sources of light by their spatial and temporal coherence. Spatial coherence allows a laser beam to be focused to a very tiny spot, enabling applications such as laser cutting and lithography. It also enables a laser beam to remain narrow over a great distance (collimation), enabling applications such as laser pointers. Temporal (or longitudinal) coherence is the capacity to have to a polarized wave at a single frequency whose phase is correlated over a relatively great distance along the beam. It allows a laser beam to emit a single color of light and can be used to produce pulses of light as short as a femtosecond. The main components of the laser are a gain medium, a mechanism to energize it, and an optical resonator, which usually consists of two mirrors. The light of a specific wavelength that passes through the gain medium is amplified by way of stimulated emission.
Compact instrumentation and (analytical) performance evaluation for laser-induced breakdown spectroscopy
Published in Instrumentation Science & Technology, 2019
Guangmeng Guo, Guanghui Niu, Qingyu Lin, Shuai Wang, Di Tian, Yixiang Duan
Compared to the continuous laser, pulsed laser is widely applied in LIBS system because of its higher energy density and property enhancement. Up until now, FLPSS laser, diode pumped solid state (DPSS) lasers, and fiber lasers are the three types of popular pulsed laser sources in LIBS devices.[20] Both the FLPSS laser and the DPSS laser are made of ND:YAG crystals as laser excitation sources, with the effect of converting 808 nm visible light to 1064 nm invisible laser. As for FLPSS laser, the laser crystal is pumped by Xenon lamp, while the DPSS laser is pumped by semiconductor diode, and it is expectable to produce the laser light when the pump light is convergent on the ND:YAG crystal through the light concentrating housing. It is usually actively or passively Q-switched for the monolithic element to generate a laser pulse with narrow width and high peak power. With respect to the fiber laser, it is optically pumped on the basis of optical fiber amplifier, and an optical fiber, doped with rare-earth elements, is employed as the gain medium. In particular, along with the properties of high beam quality, high repetition frequency and high robustness, the fiber laser is regarded as the representative of the third generation of laser. However, there is a limit on its laser energy on account of slimsy core of the optical fiber to be widely applied in LIBS. It is feasible for the FLPSS laser and the DPSS laser to emit a laser light exceeding 50 mJ. But as an emerging technology, albeit its better performance, the DPSS laser is immature and expensive in comparison to the FLPSS laser, which limit its use for the LIBS instrumentation, and hence currently the FLPSS laser is mostly used in LIBS setups.